efficient and generally safe strategy. However, supplementation
programs with a periodic mass distribution have been difficult to
sustain because of high distribution costs. Recently, food-based
interventions to increase the availability of provitamin A–rich
foods and their consumption have been suggested as a realistic
and sustainable alternative to overcome vitamin A deficiency
globally (10). However, the efficacy of carotenoid-rich foods in
the prevention of vitamin A deficiency has been questioned in
several recent studies, which reported little or no nutritional
benefit of vitamin A from the increased consumption of darkgreen or yellow vegetables (11, 12). Recently, studies have
shown that the equivalency of vegetable provitamin A carotenoids to vitamin A is in the range of 10–27 lg all-trans
b-carotene to 1 lg retinol activity (13–16). These studies showed
that food matrices greatly affect the bioavailability of vitamin A
and carotenoids.
In recent years, scientists have introduced the biosynthetic
pathway for provitamin A carotenoids into staple foods, including genetically engineered Golden Rice, which contains 1.6–
35 lg b-carotene per gram of dry rice. Golden Rice–1, which
was transformed with a construct containing a phytoene synthase
gene from daffodil, contains 1.6 lg carotenoids (0.8 lg b-carotene)
per gram of dry rice (17). Golden Rice–2 was transformed with
a construct containing a phytoene synthase gene from maize and
contains up to 35 lg b-carotene per gram of dry rice (18). Because the vitamin A equivalency of various foods and supplements varies from 2 lg b-carotene to 1 lg retinol (when
provided as a b-carotene supplement in oil) to 27 lg b-carotene
to 1 lg retinol (when provided as vegetable b-carotene) (11, 13),
and this equivalency is matrix dependent, it is important to de